The present invention relates to a technique of providing toner or developer to be applied to a recording medium such as paper or film during electrographic printing. More specifically, the invention relates to a rotating support or carousel on which are mounted modular toner or developer units, each carrying a liquid toner of a specific color to be applied to the medium.
The conventional color electrographic printing apparatus provides means for forming a plurality of superimposed component images of different colors on a recording medium to produce a composite color image. An example of such apparatus is found in U.S. Patent 4,569,584. The apparatus comprises a single recording station having a recording electrode means for forming a latent image on the recording medium and a plurality of developing units, e.g. toner fountains, adjacent either one side or both sides of recording station wherein each developing unit is provided with a respective color toner to form a color image component of the composite image. The apparatus includes means to transport the recording medium in opposite directions through the apparatus so that a first latent component image is formed at the recording head followed by its color component development. Then recording medium reversal is accomplished at least once so that a second latent component image is formed superimposed over the fist developed component image followed by its color component development. Then recording medium reversal is accomplished at least once so that a third latent component image is formed superimposed over the first and second developed component images. The process may then repeat again for as many color component images desired. At a minimum, it is preferred that four color component images be involved, i.e., magneta, cyan, yellow and black.
Different types of developer units are in use. As an example, one type is the open fountain arrangement where liquid toner is pumped to a surface forming a fountain or toner stream for engaging the recording medium. Such a development unit is illustrated in U.S. Pat. No. 4,289,092. Another type is the applicator roller and dry roller combination development unit which provides a toner film supplied to a development gap formed between the applicator roller and an opposed roller through which the medium is passed to engage the toner meniscus formed at the gap. An oppositely rotated roller down stream from the applicator roll wipes and drys the medium of excess toner. Such a development unit is illustrated in U.S. Pat. No. 4,454,833. U.S. patent application Ser. No. 06/880,772 filed 7/1/86 illustrates a development unit utilizing a single applicator/wipe roller for both applying toner to the recording medium at development apex and wiping from its surface excess toner and promoting the dry of the medium surface.
In the conventional color electrographic apparatus, the line of developer units are individually elevated to be in contact with the recording medium for the printing of the particular component color. When the printing of that color is complete, the unit is returned to a resting position, and another unit is elevated to print another color. The apparatus moves the recording medium being printed back and forth, positioning the particular medium section being imaged and developed successively above each elevated unit until all the component colors have been printed. Each unit includes its own operating components such as a toner pump, toner reservoir, applicator roller and dry roll (if a roll type development unit), etc. which are driven by attached machinery, so that the units are not readily removed and replaced.
It is known in the electrophotographic copying art to provide a removable process kit including image forming means, so that the kit may be replaced without calling service personnel. U.S. Pat. No. 4,540,268, for example, discusses such a process kit and an image forming apparatus using the kit. In one variation, the kit includes a stationary toner reservoir, containing an appropriate electrophotographic toner.
It would be advantageous to have removable development units in an electrographic printing apparatus, because the development units are susceptible to mechanical problems resulting from the wearing of parts and from the liquid toner itself, which may dry on parts of the unit or plug the orifices or passages within the development unit. These units could be easily replaced by an user or customer without the need or necessity to contact the manufacturer's technical representative. It would be further advantageous (1) to provide a more compact arrangement of the development units within the machine and (2) to provide an arrangement which would simplify the movements of the medium past the development units, such as shortening medium distance between the electrographic recording means and the development units which has the advantages of (i) reducing medium waste, (ii) rendering the medium path shorter thereby making the apparatus bed more compact and (iii) eliminating, in at least some cases, the need for a medium tracking system, such as disclosed in U.S. Pat. No. 4,569,584, to determine if the medium section being imaged and developed has expanded or shrunk so that imaging corrections can be introduced upon subsequent passes of the medium section through the apparatus to insure that each color component image being formed is properly superimposed on other component color images to form a high resolution composite color image.